netdev - Re: [PATCH net-next 02/10] net: phy: phylink: allow 10GKR interface to use in-band negotiation

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Date:   Mon, 19 Mar 2018 09:52:52 +0100
From:   Antoine Tenart <antoine.tenart@...tlin.com>
To:     Russell King - ARM Linux <linux@...linux.org.uk>
Cc:     Antoine Tenart <antoine.tenart@...tlin.com>, davem@...emloft.net,
        kishon@...com, gregory.clement@...tlin.com, andrew@...n.ch,
        jason@...edaemon.net, sebastian.hesselbarth@...il.com,
        netdev@...r.kernel.org, linux-kernel@...r.kernel.org,
        thomas.petazzoni@...tlin.com, maxime.chevallier@...tlin.com,
        miquel.raynal@...tlin.com, nadavh@...vell.com, stefanc@...vell.com,
        ymarkman@...vell.com, mw@...ihalf.com,
        linux-arm-kernel@...ts.infradead.org
Subject: Re: [PATCH net-next 02/10] net: phy: phylink: allow 10GKR interface
 to use in-band negotiation

Hi Russell,

On Fri, Mar 16, 2018 at 03:53:07PM +0000, Russell King - ARM Linux wrote:
> On Fri, Mar 16, 2018 at 11:33:43AM +0100, Antoine Tenart wrote:
> > The PHY mode 10GKR can use in-band negotiation. This patches allows this
> > mode to be used with MLO_AN_INBAND in phylink.
> > 
> > Signed-off-by: Antoine Tenart <antoine.tenart@...tlin.com>
> > ---
> >  drivers/net/phy/phylink.c | 3 ++-
> >  1 file changed, 2 insertions(+), 1 deletion(-)
> > 
> > diff --git a/drivers/net/phy/phylink.c b/drivers/net/phy/phylink.c
> > index 51a011a349fe..7224b005f0dd 100644
> > --- a/drivers/net/phy/phylink.c
> > +++ b/drivers/net/phy/phylink.c
> > @@ -768,7 +768,8 @@ int phylink_of_phy_connect(struct phylink *pl, struct device_node *dn,
> >  	/* Fixed links and 802.3z are handled without needing a PHY */
> >  	if (pl->link_an_mode == MLO_AN_FIXED ||
> >  	    (pl->link_an_mode == MLO_AN_INBAND &&
> > -	     phy_interface_mode_is_8023z(pl->link_interface)))
> > +	     (phy_interface_mode_is_8023z(pl->link_interface) ||
> > +	      pl->link_interface == PHY_INTERFACE_MODE_10GKR)))
> 
> There is no inband negotiation like there is with 802.3z or SGMII,
> so this makes no sense.

Oh, that's what I feared. I read some docs but probably will need more
:)

Anyway, the reason to use in-band negotiation was also to avoid using
fixed-link. It would work but always report the link is up, which for
the user isn't a great experience as we have a way to detect this.

What would you suggest to achieve this in a reasonable way?

Thanks,
Antoine

-- 
Antoine Ténart, Bootlin (formerly Free Electrons)
Embedded Linux and Kernel engineering
https://bootlin.com